A typical conventional converting machine used in the processing of sheets of corrugated paperboard and the like has a feed table on a support structure of the machine. The feed table includes a plurality of parallel drive shafts extending between and rotatably mounted to opposite sides of the support structure, multiple rotatable feed wheels spaced along and clamped about the drive shafts for rotation with the shafts, and a plurality of spaced apart grates or plates overlying some of the feed wheels and disposed between others. The sheets of paperboard are loaded in a stack form on the support structure of the machine so as to overlie the feed table. Upper portions of the feed wheels protruding above the plates engage the bottom surface of the lowermost one of the stacked sheets. Rotation of the drive shafts, in turn, rotates the feed wheels through a cycle of controlled acceleration followed by deceleration to cause feeding by the wheels of the lowermost sheet from under the stack to the nip of a pair of feed rolls of the machine located adjacent to the feed table, which feed rolls then transfer the sheet to other downstream processing stations of the machine. Some representative examples of such converting machines are disclosed in U.S. Pat. No. 4,045,015, U.S. Pat. No. 4,614,335, U.S. Pat. No. 5,184,811 and U.S. Pat. No. 6,609,997.
In most of these feed tables, the feed wheels have cylindrical-shaped hubs with annular or ring-shaped treads supported thereabout and commonly made of stretchable polyurethane material which provides a high coefficient of friction gripping peripheral contact with the surface of the sheet. The sheets may need to be accelerated from 0 to 200 fpm in a fraction of a second (eg, at feed rates of up to 400 sheets/min). As it is typically important that the sheet is fed at the correct instant in time (relative to the cycle of the machine) and at the correct speed (to match the machine speed), uniform gripping and wear become the main requirements of the feed wheel treads. As high coefficient of friction gripping materials undergo normal wear, their dimensions change which, in turn, changes the speed at which they feed the sheet. Furthermore, the degree of wear of treads of different wheels may vary and thus the wear may be uneven across the feed table. This is a significant problem since if wear (or lack of wear) occurs more on the treads of some wheels than others the tendency is for the less worn, thus larger diameter, wheels to push that side of the sheet forward faster than more worn, thus smaller diameter, wheels which will increase the likelihood of skewed sheet feeding and pulling on that side of the sheet introduced first to the feed rolls which will further pull the sheet at an angle.
Thus, as they become worn, the feed wheel treads need replacing which requires a certain amount of disassembly and reassembly of the feed table depending upon the type of tread in use. For example, in the case of a more common continuous, or full ring style, tread, the amount of disassembly will typically involve: (a) removal of the plates covering the wheel treads; (b) decoupling the driven shafts from a gearbox and removal of their bearing supports; (c) removal of the driven shafts from the machine; (d) cutting off or socking (forcing) all the treads from the hubs and shafts; (e) then socking on replacement treads from the ends of the shafts and over one or more hubs; and (f) reassembly of the driven shafts and plates to the feed table. These disassembly and reassembly steps typically take 1–2 hours for two mechanics/fitters and require the same amount of production downtime (unscheduled if feed problems are being experienced.)
An alternative to the continuous, or full ring style, tread that has been used to reduce the requirement for performance of some of the aforementioned disassembly and reassembly steps is a discontinuous, or split ring style, tread produced by a planar or straight radial slit or cut through the tread at one location. This discontinuous, or split style, tread permits a wrap around removal and fitting of the tread to a modified hub without the need to sock each tread on the hub. The hub is modified by providing a plurality of peripheral recesses spaced circumferentially thereabout into which fit a plurality of cylindrical shaped locking lugs extending inwardly of the tread body at ninety degree intervals and projecting along axes extending generally parallel to a central axis of the feed wheel.
With respect to this alternative, the grates or plates of the machine that cover most of the space around these treads still require removal to enable maintenance personnel to grip and pull up the worn tread, typically from a side of the tread, to remove them. Thus, this alternative has not been widely adopted by the industry as it still requires some disassembly and reassembly and also lends itself to feed problems as the gap at the planar radial split or join of the tread has a tendency to open up due to the considerable loads that the treads are subjected to as they grip and move the sheet. Thus, to date, the continuous, or full ring style, tread remains the more popular one.
However, further complicating matters, because of the aforementioned uneven wear of the feed wheel treads and the requirement that the replacement of even one tread will necessitate the aforementioned steps involved in machine disassembly and reassembly, the replacement of all treads is typically periodically scheduled and carried out even though some treads will be worn less than others and thus are prematurely discarded. The most common technique of deciding when treads need to be replaced is when it is observed that skewing or loss of register of the sheets has become unacceptably high. Another less common technique is to attempt to measure the height that the treads protrude above the feed grates or plates, which is a laborious and thus inherently inaccurate process.
Further, it should be pointed out that the continuous, or full ring style, tread relies solely on friction (from the undersizing of the inside diameter of the shoulder of the tread relative to the outside diameter of the shoulder of the hub) to keep the tread from indexing (slipping) on the hub. Indexing of the tread on the hub will adversely affect the accuracy of the registration of the sheet.
Consequently, a need still exists for an innovation which will provide a solution to the aforementioned problems of the prior art feed wheels without introducing any new problems in place thereof.